Polycarbonate resins are resins that exhibit excellent heat resistance, mechanical properties and electrical properties, and are widely used in, for instance, automotive materials, electrical and electronic device materials, housing materials and materials for producing components in other industries. In addition, polymer alloys with other thermoplastic resins have been developed, and of these, polymer alloys with styrene-based resins such as ABS resins are less expensive and enable better molding processing properties and impact resistance than polycarbonate resins, and are widely used as parts of electrical and electronic devices and OA information devices, such as computers, personal computers, portable terminals, printers and copying machines.
ABS resins used in polycarbonate/styrene-based resin compositions are often produced by means of emulsion polymerization for reasons such as cost, applicability to a wide range of products and facilitating quality improvement by increasing rubber content, but bulk polymerized ABS resins are used for reasons such as wet heat resistance, as disclosed in PTL 1 (see claim 8; paragraph [0024]).
Styrene-based resins by bulk polymerization are expensive, and use of products obtained by means of emulsion polymerization has been considered in order to reduce costs, but polycarbonate resin compositions containing emulsion polymerized styrene-based resins have the drawback of wet heat resistance being poor. Furthermore, problems occur, such as mold contamination due to mold deposits during molding being significant, and the amount of gas generated being large.
It is thought that these problems are caused by components derived from emulsifiers used during emulsion polymerization or oligomer components remaining in styrene-based resins, and although the mechanisms thereof are not sufficiently clear, it is thought that components derived from emulsifiers affect hydrolysis of polycarbonate resins and cause a deterioration in wet heat resistance, and that oligomer components cause mold contamination and gas generation.
Emulsion polymerized ABS resins are generally produced by emulsion polymerizing a butadiene using mainly a higher fatty acid soap or rosin acid soap as an emulsifier and using a water soluble polymerization initiator so as to obtain a polymer latex and then polymerizing styrene and acrylonitrile or the like in the presence of the polymer particles and an emulsifier so as to obtain an ABS polymer latex, and then adding a coagulating agent such as an inorganic acid or a divalent metal salt to the ABS polymer latex, washing and drying. For reasons of economy, the emulsifier is not completely removed in the washing step, and unremoved emulsifier remains in the product.
Consideration has been given to thoroughly pre-washing ABS resin raw materials used in emulsion polymerization, but it was found that even if thorough washing is carried out using water or an organic solvent such as methanol, emulsifier components contained in the resin cannot be easily removed.